SYNTHESIS AND STRUCTURE DETERMINATION OF GIBBERELLIN-DERIVED ANTHERIDIOGENS FROM FERN GAMETOPHYTES OF THE LYGODIUM GENUS

Two successful and two unsuccessful synthetic routes are described for the conversion of commercially available fungal gibberellins to the a ntheridiogen GA(73) methyl ester (5), originally isolated from gametop hytes of the fern Lygodium japonicum. The more efficient route began w ith the Birch reduction of either the GA(7) derivative (31) or methyl gibberellate 3,13-dimesylate (32) to give the Delta(1(10),16)-diene ac id (33), which was converted into the Delta(1,9)-diene acid (40) by me ans of a four step procedure. This intermediate could be selectively h ydrogenated to the Delta(9)-ene derivative which underwent iodolactoni zation and then elimination of HI to afford enone (29), Wittig methyle nation of which furnished the target antheridiogen (5). In addition, ( 29) was functionalized at C12 by free radical bromination to give acce ss to the 12 beta-hydroxy derivative of (5), i.e. (6), a new antheridi ogen isolated from Lygodium circinnatum.